utility: added FilePath abstraction and rewrote data management to use it

The utility class FilePath wraps an instance of boost::filesystem::path. Using FilePath allows for easy comparision of
file paths on different platforms using absolute or relative paths. Whereever file paths are compared, this wrapper
should be used.

src/lib/data/location/TokenLocation.cpp

@@ -84,7 +84,7 @@ unsigned int TokenLocation::getLineNumber() const
 	return m_line->getLineNumber();
 }
 
-const std::string& TokenLocation::getFilePath() const
+const FilePath& TokenLocation::getFilePath() const
 {
 	return m_line->getFilePath();
 }